In an automatic analyzer such as a biochemical automatic analyzer, for the component analysis of a biological sample (blood serum, urine, etc.), the sample and a reagent are brought into reaction and changes in the color tone and the turbidity caused by the reaction are optically measured by a photometric measurement unit such as a spectrophotometer.
For the reaction of the sample and the reagent, dispensation of the sample and the reagent from vessels storing them to a reaction vessel has to be carried out. Therefore, such an automatic analyzer is equipped with a dispensation device capable of automatically performing the suction of a sample/reagent from a vessel storing the sample/reagent and the discharging of the sample/reagent into a reaction vessel.
In a sample dispensation device for dispensing a sample from a sample vessel to a reaction vessel, dispensation abnormality can occur due to various factors. The sample dispensation device has a probe for sucking in and discharging the sample. The clogging of the probe caused by suction of solid foreign objects (e.g., fibrin) is a frequent cause of the dispensation abnormality. The clogging of the probe makes it impossible to accurately dispense the prescribed amount of sample to the reaction vessel and acquire reliable analysis result.
Further, when an air bubble or a liquid membrane exists on the liquid surface of the sample, the air bubble or the liquid membrane can be detected as the liquid surface. This disables the suction of the necessary amount of sample and causes the dispensation abnormality.
In order to avoid the dispensation abnormality caused by the existence of an air bubble or a liquid membrane, it is possible to increase the immersion depth of the probe in the sample. However, increasing the probe's immersion depth in the sample can lead to an increase in the contamination and an adverse effect on the analysis result.
Therefore, the operation of the probe is generally controlled by the following method in order to reduce the probe's immersion depth in the liquid as much as possible: First, the surface of the liquid in the vessel is detected. The downward movement of the probe is stopped at a position where the tip end of the probe is situated slightly below the liquid surface. Thereafter, a prescribed amount of liquid is sucked into the probe.
As a method for detecting the liquid surface of the sample, the capacitance change method (detecting a change in capacitance when the probe makes contact with the liquid surface) is the most commonly used. However, if the aforementioned air bubble or liquid membrane exists on the liquid surface when such a liquid level sensor is used, the liquid level sensor can erroneously detect the air bubble or the liquid membrane as the liquid surface and cause the dispensation abnormality.
Many technologies have been proposed as means for judging the occurrence of the above-described dispensation abnormality, in which a pressure sensor is arranged in a dispensation channel including the sample probe and the dispensation abnormality (e.g., the clogging of the sample probe) is detected based on pressure fluctuation.
In a technology disclosed in Patent Literature 1, data generated from time-series data of the pressure when the suction was performed normally is used as reference data. Meanwhile, time-series data of the output value of the pressure sensor at the time of the suction is used as comparative data. Abnormality in the suction is detected based on the Mahalanobis distance calculated from the reference data and the comparative data.
According to the technology described in the Patent Document 1, the reference data is prepared corresponding to each dispensation condition including the dispensation quantity, and thus the abnormality can be detected accurately even in different dispensation conditions. Further, since the abnormality detection is carried out by calculating the Mahalanobis distance based on the time-series data of the pressure across the entire period from the start of the suction to a time after the end of the suction, not only an abnormality caused by a particular factor but also abnormalities caused by a variety of factors can be detected.